Interpretive Summary: Increased plasma membrane phospholipid disorder in the plasma membrane and maturation of the acrosome on the sperm head must occur before the sperm can fertilize the egg. Flow cytometry with fluorescent stains was used to determine if boar semen liquid storage for 1 or 5 days at 17 degrees Centigrade or frozen storage of caused excessive phospholipid disorder in the plasma membrane and excessive maturation of the acrosome. Basal phospholipid disorder and acrosome maturation in sperm from freshly collected semen was less than 2.2% and increased only a small amount after liquid storage for 5 days or after freeze-thawing (3-8%). However, liquid storage and freeze-thawing did impair experimental induction of phospholipid disorder and acrosome maturation indicating potential problems with sperm fertility. These techniques may be useful to monitor sperm quality or to predict fertility.

Technical Abstract:
Flow cytometry was utilized to determine whether short (d1), long term hypothermic liquid storage (d5), or cryopreservation of boar spermatozoa 1) caused changes in plasma membrane phospholipid disorder (PLD) and acrosome exocytosis (AE) in viable sperm populations associated with an advanced stage of capacitation or acrosome status and 2) facilitated or inhibited the induction of capacitation and the acrosome reaction. Merocyanine with Yo-Pro-1 and peanut agglutinin-FITC with propidium iodide were used to identify PLD and AE, respectively. The incidence of basal sperm PLD and AE in fresh semen was very low (1.1 and 2.2%, respectively) and increased (P less than (LT.) 0.05) only a small amount in d5 and cryopreserved semen (3-8%). Compared to no bicarbonate, incubation with bicarbonate increased PLD, but the response was greatest (P LT. 0.05) in fresh sperm (52.3%) compared with d1 (36.6%), d5 (13.9%), and cryopreserved sperm (13.6%). Incubation with calcium ionophore A23187 increased AE in spermatozoa, but the response was less (P LT. 0.05) for fresh (34%) and cryopreserved (27%) semen than for d1 (45%) and d5 (57%) semen. In summary, hypothermic liquid storage and cryopreservation of boar spermatozoa did not advance capacitation or acrosome reaction status in viable spermatozoa.